1. Field of the Invention
The present invention relates to a comb copolymer suitable for use as an acrylic elastomer which is excellent in transparency, weatherability and mechanical properties; to a methylmethacrylate (co)copolymer blended with the comb copolymer; to a comb copolymer as an acrylic resin which is excellent in transparency, weatherability, gloss and light resistance; and to a preparation method of a high molecular weight comb copolymer useful as a molding material comprising the above comb copolymer.
2. Description of the Prior Art
Methyl methacrylate polymer and copoymers have been conventionally used for cast sheets, injection-molded articles and extruded products as resins which are excellent in transparency, gloss and weatherability. On the other hand, these resins are hard and brittle and it is hence difficult to prepare, for example, films and sheets from them. Consequently, the field of application of these resins has been limited until now. In order to eliminate the disadvantages of hardness and brittleness, various methods have been proposed such as a method for blending elastomers with the methyl methacrylate (co)polymers and a method for grafting methyl methacrylate on elastomers. The method for grafting methyl methacrylate on the elastomers exhibits a particularly remarkable effect. Accordingly, various proposals have been made about the kinds of the elastomers used and the methods for graft polymerization. These proposals include, for example, a method for using diene polymers such as polybutadiene as the elastomers and a method for using acrylic elastomers. The former method, however, has a drawback in that it causes a severe decrease in weatherability of resulting polymers due to double bonds contained in the elastomers. The latter method is also disadvantageous in that a large amount of the acrylic elastomers must be used in order to obtain a satisfactory effect, because the latter method is less effective in the improvement than the former method, which situation inevitably leads to a decrease in transparency and gloss of the resulting polymers.
On the other hand, styrene-diene block copolymers and polyester-polyether block copolymers have already been developed for the materials of thermoplastic elastomers. Acrylic elastomer materials, however, have not yet proven satisfactory, although there has been a need for these materials in view of their excellent transparency and weatherability.
In order to develop acrylic elastomers, anion living polymerization has also been tried as in the case of the styrene-diene block copolymers. However, satisfactory results have not yet been obtained because of the difficulty in completely carrying out living polymerization of acrylic esters. A method for grafting methacrylic esters on cross-linked acrylic rubber has also been investigated. However, satisfactory products have not been developed, because the processability and transparencey of the resulting copolymers has decreased with the increasing ratio of the acrylic rubber component.
In order to enhance the functions and performances of polymeric materials, the development of block copolymers and graft copolymers has been carried out until now. Since technical progress has recently been made in the synthesis of oligomers and polymers having a polymerizable functional group at one end of the main chain, attention has been focused on the development and application of comb copolymers derived from these oligomers and polymers. Preparation of comb copolymers from these oligomers or polymers and common vinyl monomers is generally carried out by a solution polymerization method where both materials are dissolved with a polymerization initiator and copolymerized in a suitable solvent. Bulk polymerization or suspension polymerization may also be conducted using the vinyl monomer dissolved with the above oligomers or polymers and the polymerization initiator.
The above solution polymerization method has the advantage of allowing the polymerization to progress with ease. On the other hand, since there is the problem that the method is liable to cause chain transfer reaction into the solvent, comb copolymer having high molecular weights are difficult to produce. Consequently, it has been difficult to employ products obtained by solution polymerization for uses requiring mechanical properties, for example, elastomers and molding materials.
The method for conducting bulk polymerization or suspension polymerization by using the vinyl monomer dissolved with the oligomers or the polymers has the advantage that high molecular weight copolymers can be obtained with ease as compared with solution polymerization method. On the other hand, there is the problem that comb copolymers having high ratios of the oligomer or polymer components are difficult to obtain because the solubility of said oligomers or polymers in the vinyl monomer is not so high.
As described above, the prior art aimed at manufacturing copolymers having specific structure and thus having specific properties, that is, comb copolymers but provided merely copolymers having either low molecular weights or high ratios of the vinyl monomer components. Consequently, comb copolymers having the desired characteristics have not yet been obtained.